The controlled application of fluid pressure to a load utilizing, for example, a pressure converter at whose pressure output side, the pressure converter is connected by one check valve to a source of fluid and by another check valve to the load, utilizes the repeated strokes of the pressure converter to allow a fluid to b drawn into the output side through the first check valve and then to be discharged at higher pressure through the second check valve.
In order to pressurize liquid for pressure testing and like applications, high pressure plunger pumps have generally been used and this is the case for the pressure testing of pipes as well.
Since the reciprocation of the piston for pressurizing the pipe can result in the generation of an oscillation which may represent a deviation from a test protocol, such oscillations cannot be tolerated for pipe-testing purposes. The pressure medium used for the pipe testing is generally water and optionally a water-based emulsion and since a control valve in frequently provided to connect the piston pump with the pipe to be tested, that valve may be subject to wear from substances which may be entrained in the water or water emulsion, like scale or the like.
When pressure converters were provided for the testing of pipe and the like, the pressure regulation could be effected at the oil side of the system to eliminate wear of the control valve by the water or water emulsion. In addition such systems did not have oscillations during pressure buildup and while the pressure was maintained.
However, the volume required at the water side was invariably far in excess of the compression volume of the converter and thus for practical reasons very large and hence expensive pressure converters had to be us d. In addition, the pressure converters gave rise to extreme fluctuations in the pressure medium. These drawbacks not only applied to pipe-testing presses but wherever the unit was used to build up a fluid pressure for a load.